In order to meet the current stringent reliability and meantime before failure (MTBF) requirements demanded by the automotive, industrial and aerospace industries, position sensors must be based on a non-contact design approach. This is in order to minimize the wear and tear on internal components. And especially for automotive use, the design must be suited for low cost, high volume, and high reliability. One type of non-contacting sensor utilizing a so called screened inductance is illustrated in U.S. Pat. No. 4,986,124. Here a pair of drive and sense windings on the same printed circuit board have a conductive screen adjacently mounted on an axis or pin, which when rotated can "shade" the sense winding. As summarized by the above patent, it operates as follows: (column 12, line 33) "Transducer output from screened inductance sensor is essentially an amplitude modulated carrier frequency. The carrier component is normally removed in the first stage of signal processing by synchronous modulation. The transfer function relating the input variable [that is rotation ] to signal magnitude is the most important characteristic of any position measuring device."
However, the use of a detected amplitude, especially for automotive and industrial applications is not suitable. Such amplitude is affected by the separation between transmitter and receiver and also the power level of the transmitted signal. Errors resulting from the foregoing uncertainty will not provide acceptable performance.